1a.Objectives (from AD-416)
Knowledge of the effects of cropping systems on selected soil properties is needed to optimize productivity and develop sustainable agricultural systems. The effects of alternative dryland and irrigated crop and livestock systems on water infiltration, soil aggregation, and other soil properties will be defined through the following sub-objectives. 1.1 Determine the effect of agricultural management practice factors such as crop type, irrigation amount and type, tillage intensity, and residue cover on water infiltration aggregate stability carbon sequestration, soil microbial community structure, and enzymes that affect soil function. 1.2 Validate and further refine the Soil Conditioning Index and Soil Management Assessment Framework to assess the sustainability of management practices and systems.

Wind erosion and dust emissions are controlled by biological and physical processes and characteristics that must be determined to develop successful methods of dust mitigation. We will investigate basic biological and physical processes and characteristics of wind erosion and airborne dust needed to develop mitigation strategies using the following sub-objectives. 2.1 Quantify total airborne soil mass transport and fine particle dust emissions as affected by soil texture and cropping system. 2.2 Determine enzyme activities, microbial community composition, and chemical characteristics of fine particle dust from agricultural soils to identify the sources and origin of dust. 2.3 Validate and further refine the time fraction equivalent method for determining the threshold condition for soil movement in the field under natural wind and soil conditions. 2.4 Identify morphological traits that promote resistance to injury caused by abrasion of plants by sand particles during wind storms and determine the most resistant varieties of selected common crops.

1b.Approach (from AD-416)
Agricultural management practice factors such as crop type, irrigation amount and type, tillage intensity, and residue cover will be correlated with water infiltration, aggregate stability, carbon sequestration, soil microbial community structure, and enzymes that affect soil function. The soil conditioning index and soil management assessment framework, used to assess the sustainability of management practices and systems, will be evaluated and refined. Total airborne soil mass transport and fine particle dust emissions as affected by soil texture and cropping systems will be quantified. Enzyme activities, microbial community composition, and chemical characteristics of fine particle dust from agricultural soils will be used to identify the sources and origin of dust. The time fractions equivalent method for determining the threshold condition for soil movement in the field under natural wind and soil conditions will be evaluated and further refined. Morphological traits that promote resistance to injury caused by abrasion of plants by sand particles during wind storms will be identified and the most resistant varieties of selected common crops will be determined.

3.Progress Report
Wind erosion and dust emissions are affected by surface soil properties and management. Knowledge of how these factors affect wind erosion is needed to develop predictive models and control practices to limit emissions. A field wind tunnel was developed, calibrated, and used to determine fine dust emissions on cropland and rangeland. Initial testing of the field wind tunnel demonstrated dust emissions were very sensitive to surface soil properties such as soil texture, dry and wet aggregate stability, and surface micro-roughness. This research will include a study in the use of rare earth elements to identify the source areas of mobilized sediment. At the current time we are using laboratory methods to determine the transport of surface-applied rare earth element solutions into soils with different particle size distributions. The information obtained will be used to refine our field use of these materials at a study at the Sevilleta National Wildlife Refuge in New Mexico next spring. Dust emission tests using the field wind tunnel comparing bare crusted fine-textured soils with sites that have been exposed to cattle traffic showed large increases in fine dust emissions after disturbance of the surface. This research clearly shows that soil properties and management are important factors controlling fine dust emissions. The time fraction equivalent method provides a means of determining threshold from data supplied by a sampling system that continuously collects wind and saltation data while left unattended in the field for extended periods. Last year a camera system was developed that allows the collection of a series of high resolution images of surface conditions at remote sites over extended periods. Measurements taken over a 7-month period on the high plains of the Llano Estacado of West Texas suggest that sand movement tends to occur more frequently during daylight hours, with a peak in aeolian activity occurring in the afternoon between 1400 and 1500 Local Standard Time (LST). We examined the effects of wind and wind-blown sand abrasion damage on cotton seedlings in a suction-type laboratory wind tunnel over three separate experiments. Increasing plant damage caused by sand abrasion treatment resulted in preferential biomass partitioning to the damaged stems rather than roots immediately following sand abrasion damage while a much more stable allometric allocation of biomass among plant organs was observed after 2 weeks. We did not find differences in responses among the three cotton cultivars tested. These findings suggest that cotton breeders selecting for traits that lend resistance to and/or recovery from sand abrasion should focus on specific physiological traits related to photosynthetic rate adjustments after abrasion.

4.Accomplishments
1.
Estimating Wind Erosion Using Isotopes: Wind erosion is a soil-degrading process that threatens the sustainability of agriculture in semi-arid environments. For the past two decades, scientists have used cesium, 137Cs, a man-made isotope distributed globally in stratospheric fallout during the period from 1956 to 1964, to evaluate cropping systems and soil management effects on wind erosion rates. However, the relative short half-life of 30 years for 137Cs will soon limit its usefulness as a soil-borne tracer and another artificial isotope with a longer half-life must be found and validated. Using split soil samples from fields with documented wind erosion and deposition histories and for which existing models have been calibrated using 137Cs activities, we have shown that an isotope of plutonium, 239+240Pu, is an ideal tracer for quantifying soil redistribution. We believe that our results differ from previous attempts to use 239+240Pu as a tracer for water erosion due to the very low organic matter contents of our soils. Since low organic matter content soils are common in semi-arid and arid regions where wind erosion threatens agricultural sustainability, this research will provide scientists with an important new tool to quantify the amount of wind erosion in dry regions and will have wide application around the world.

2.
In search of sustainable agricultural systems for the Llano Estacado of the U.S. Southern High Plains: Bacterial diversity, a measure of the different kinds of bacteria in the soil, is an important tool to evaluate how agricultural practices and land use affect soil processes, but it has had limited use due to the current expensive and labor-intensive methodology used. We developed a new bacterial tag diversity method to characterize the bacterial diversity of Pullman soils under four systems: (1) a pasture monoculture for livestock production, (2) a diverse mixture of grasses in the Conservation Reserve Program, (3) a cotton-winter wheat-corn rotation, and (4) the typical practice of the region, which is continuous monoculture cotton. Bacteria associated with specific soil processes were identified and related to different cropping systems. We identified higher bacterial diversity in soils with systems that offered more soil protection with grass, conservation tillage, and/or under cotton in rotations with other crops than with continuous cotton. The technique that we developed was an improvement over previous work with soils using the traditional method and will allow scientists to more easily determine the sustainability of land management on soils.